The present invention relates to bearing and shaft assemblies and more specifically relates to shafting having a non-circular cross section which is received in bearings having an inner race provided with a matching shaped opening receiving the shaft.
On known machines, agricultural balers for making large round bales, for example, non-circular section shafting has been used to provide stub shafts or end-shafts in live-shaft rollers. The live-rollers can then be used for providing input and output torque drives without requiring secondary shaft finishing operations such as spline hobbing, etc. (for example, see U.S. Pat. No. 5,448,944, granted to Line et al.), and to address the many shortcomings of using bearings with eccentric locking collars on round shafts. However, there is a continuing issue with two phenomena at the joints between these shafts and bearings, namely: (a) rotational knock and (b) axial creep.
Rotational knock, as concerns shafting having a multi-facet cross section, is a result of excessive clearance between the across-flats dimension on the shaft and the bearing bore. Rotation of the shaft causes the shaft flats to shift in reaction to the load resultant, and if sufficient clearance exists, an audible knocking noise is perceived. This can be amplified by adjacent structural or surrounding metal shielding to the extent that it is objectionable to customers or passersby. Negative impressions of the machine can result, and, while it is not known whether premature bearing failure might result, there is no doubt that in extreme cases continued sliding of the loose fit during operation will result in wear further increasing the clearance and eventually requiring the replacement of either the bearing, or the shaft, or both.
Axial creep is due to a combination of clearance between the across-flats dimension of the shaft and bearing bore, along with some angularity or non-parallelism existing between the axis of the shaft and the bearing axis. Rotating the shaft under these conditions can cause the shaft to incrementally crawl or creep with each successive bearing flat as it is encountered. The result of this situation is that axial loading will be conveyed to the bearing. In the case of ball bearings, which are not designed to withstand substantial axial loads, the service life of the bearing may be shortened. Also, there can be sufficient axial force generated by this phenomenon that structural members can be flexed through repeated cycles to the point of causing fatigue failures. There can also be objectionable slamming noise caused when the unit is shut off, which releases the torque in the system, and the friction is broken at that point, allowing the supporting members to return to their original positions.
Currently, the above problems encountered with non-circular section shaft and bearing combinations are addressed by closely controlling the dimensions on the shaft and bearing bores so as to limit the clearances involved, and to use a chemical compound during the assembly process for filling the remaining clearance with a resilient material. The successful combination of controlling clearances together with using a chemical compound has had mixed results. Due to random combinations of parts, it has been demonstrated that fits will occur which result in gaps that are beyond the capability of the chemical compound. Continuing efforts to achieve closer tolerance controls have not proved successful and it appears that significant cost increases would be required to guarantee closer tolerances. Furthermore, even if the tolerances are kept within those with which the chemical compound will be effective, other issues arise. First, the cleanliness of the shaft and the bearing at the joint is critical to getting the chemical compound to harden as the ions of the cleaned metal are a catalyst in the process. Second, application of the chemical compound onto the shaft, and then installing the bearing onto the shaft tends to wipe the bulk of the compound off the shaft so it is not available in the formed joint. This is wasteful, and makes the process ineffective. Third, a good joint is difficult to separate for the purposes of service, e.g., when a bearing needs to be replaced. Last, some individuals are sensitive to the chemical compound and may develop a skin rash if they come into contact with the compound. Thus, protective equipment and extra care is required to avoid coming into contact with the chemical compound.
According to the present invention there is provided an improved shaft and bearing combination.
An object of the invention is to provide a shaft and bearing combination which does not require close tolerances and/or a chemical compound to eliminate rotational knock and/or axial creep.
A more specific object of the invention is to provide a combined shaft and bearing combination wherein the inner race of the bearing is clamped so as to prevent it from undergoing radial movement, thereby eliminating rotational knock. Specifically, the clamping is effected by using a fastening device, such as a bolt in the end of the shaft or a nut on the end of the shaft, to provide the clamping action on a properly selected stack-up of washers and/or shims, the bearing and/or spacers and/or shaft length.
Yet another object of the invention is to provide a combined shaft and bearing combination, as set forth in the immediately preceding object, wherein the bearing is mounted for axial movement so axial loading of the bearing during assembly or operation is avoided. In accordance with a first embodiment, this object is achieved by mounting the bearing to a carrier that is mounted to a fixed bearing support for some axial movement relative to the support. In accordance with a second embodiment, the carrier is eliminated and the bearing is mounted in a housing mounted to a bearing mounting plate or support that is strong in the plane which is perpendicular to the shaft, but is relatively soft, and able to flex in the axial direction of the shaft, thereby limiting the axial load which is transmitted between the shaft and the frame, via the bearing.
These and other objects will become apparent from a reading of the ensuing description together with the appended drawings.